Exemplary embodiments of the present disclosure relate to reducing a start-up time of a steam turbine, and more particularly, to a steam turbine capable of being operated with the temperature of a rotor of an intermediate-pressure turbine increased as high as possible before rotation of the steam turbine starts in a state in which thermal stress of the intermediate-pressure turbine is minimized.
Generally, with regard to start-up of a steam turbine, if the time it takes to restart the steam turbine that is in an interrupted state is increased, a large difference between the temperature of a turbine rotor and the temperature of supplied steam may be caused. Due to this, the rotor provided in an intermediate-pressure turbine may be deformed or damaged by thermal stress in an initial operation. Therefore, particular attention to this is required.
As start-up and restart of the turbine are repeated many times, the lifetime of the turbine rotor is reduced. In this regard, various methods of pre-warming the steam turbine, prior to the operation thereof, to solve problems caused by thermal stress of the rotor have been proposed.
For example, a conventional steam turbine uses a method of performing pre-warming in such a way that steam is supplied into a high-pressure casing and the interior of the high-pressure casing is retained for several hours at an allowed maximum pressure.
The pre-warming operation of such a conventional method has been mainly used as a method for preheating the rotor because it has advantages in that both a rotating part and a stationary part can be preheated before start-up and the rotating part and the stationary part can be prevented from coming into contact with each other due to abnormal deformation of the turbine rotor or the casing.